Control circuits of the above kind operate especially to reduce the development of noise and heat of the fuel pump of motor vehicles during part load operation and idle operation by reducing the speed of the pump. Such a control circuit is disclosed in International Patent Application PCT/DE87/00095, filed on Mar. 5, 1987, and designating the United States of America. The control circuit disclosed in this publication contains a unit which provides that the fuel pump operates with at least a minimal speed and thereby maintains a corresponding minimum fuel supply. This is especially required for internal combustion engines equipped with fuel injection since a minimal delivery rate must always be provided by the electric fuel pump for all fuel injection systems to build up the system pressure.
It is generally known to protect an internal combustion engine against impermissibly high speeds by including a speed limiting device. For this, two different possibilities are known.
In the first possibility, a speed limitation is achieved by switching off the fuel injection above a predetermined maximum speed. For this purpose, an appropriate control function must be present in the particular injection control.
The second possibility of providing a speed limitation is carried out in spark-ignition engines by switching off the ignition. This leads to an undesired high pollutant emission and unfavorably influences a catalyzer should one be present.